1. Field of the invention
The present invention relates, generally, to motor vehicle headlamps and, more specifically, to a projection lens for use in an LED module of a motor vehicle headlamp
2. Description of he Related Art
Motor vehicle headlamps are well known in the related art. Conventional headlamps may include a light source in the form of an LED matrix, including numerous LED chips disposed in a matrix, adjacent to and/or above one another (also referred to as matrix headlamps). The LED matrix may include a single row or column having numerous LED chips, or of numerous rows or columns disposed above or adjacent to one another, each having numerous LED chips. Matrix headlamps generate a light distribution on a road surface in front of a motor vehicle, which has numerous sub-light distributions in the form of pixels or strips, disposed adjacent to or above one another. Each LED chip normally generates its own sub-light distribution. With a targeted activation, in particular an on/off switching or dimming of the individual LED chips of the matrix light source, it is possible to influence the shape and the intensity of the light distribution. In this way, a matrix headlamp can be used to generate an adaptive light distribution without moving parts. In particular, it is possible to generate a basic low beam light distribution having a horizontal light/dark border, a conventional low beam light distribution having an asymmetrical light/dark border, a high beam light distribution, a partial high beam light distribution in which targeted regions are removed from the light distribution where other road users have been detected, or a marker light distribution in which objects detected on the road surface in front of the vehicle are illuminated in a targeted way. Matrix headlamps are known in the prior art in different embodiments, such as in published application numbers EP2306073A2, EP2306074A2, EP2306075A2, and DE102008013603A1. Further, approaches specifically for so-called “strip-headlamps” are known in the prior art, such as in published application numbers DE102011077132A1 and DE102011077636A1, with which the generated light distribution includes numerous strip shaped sub-light distributions, disposed adjacent to one another. Approaches for designing a color-correcting projection lens for matrix headlamps are known from DE102010626B4. It is proposed in EP2280215A2 that the homogeneity and the resolution of the image be improved through the use of numerous LED modules in a headlamp. An individual projection lens (or secondary lens) is allocated to each primary lens, thereby necessitating that two light source modules, at least two primary lens modules, and at least two secondary lens modules be combined for the known headlamp. Thus, at least two light exit surfaces for each matrix headlamp are visible from the outside. A so-called “compound eye” headlamp module is obtained. The strip-shaped sub-light distributions projected onto the road surface have a relatively large angular width of at least 2° horizontally, or even significantly larger. The superimposing of wide strips of this type improves the homogeneity of the light distribution, but reduces the obtainable resolution. The known headlamp requires at least two complete light modules that are independent of one another for each headlamp, wherein each light module has an LED matrix, a primary lens and a secondary lens. Thus, a headlamp of this type includes at least two light sources, two primary lenses, and two secondary lenses. With all of the matrix headlamps known from the prior art, there is, however, the problem that there are color and intensity fluctuations in the resulting light distribution. These are caused mainly by the dispersion (a change in the refraction index for optical materials in relation to the light wavelengths) and imaging errors in the projection lens. The color fluctuations occur in particular at the edges of the individual sub-light distributions.